High efficient crosslinking of gelatin and preparation of its excellent flexible composite film using deep eutectic solvent

To overcome the gelation of gelatin at low temperatures, solve the brittleness of gelatin-based films and improve the reaction efficiency between the components, a facile design strategy is proposed for preparing gelatin/polyvinyl alcohol composite films (Gel-PVAs) with excellent flexibility. During the preparation process, sodium acetate trihydrate/urea deep eutectic solvent (SAT/U-DES) was introduced to dissolve the gelatin, which not only exhibited the higher crosslinking efficiency but also induced the plasticizing effect to the composite film. When the DES mass fraction was 60%, the solubility of the gelatin was up to 25%, and gelation did not occur at room temperature. In addition, the elongation at break of the Gel-PVA60 film reached up to 654%, which was a 631% increase when compared with that of the Gel-PVA0 film. These remarkable properties were due to the formation of new H-bonds with the groups in gelatin molecules induced by SAT/U-DES, which limited the reformation of the gelatin structures after cooling and improved the flexibility and ductility of the film. Moreover, the destruction of interchain interactions between the gelatin molecules allowed more carboxyl groups to react with PVA in the crosslinking modification system, which resulted in an improvement of the reaction efficiency without external catalysts.